Cut around base of iron grate (5)
I believe the answer is:
gnash
'grate' is the definition.
(gnashing is a kind of grating)
'cut around base of iron' is the wordplay.
'cut' becomes 'gash' (gash is a kind of cut).
'around' indicates putting letters inside.
'base of' suggests the final letters.
The last letter of 'iron' is 'n'.
'gash' enclosing 'n' is 'GNASH'.
(Other definitions for gnash that I've seen before include "Hangs (anag.)" , "Grind away" , "champ" , "grate" , "Strike one's teeth together in rage" .)